This invention relates to an improved snowplow apparatus and more particularly to a snowplow apparatus in which the snow clearing blade is capable of passing over small obstacles projecting from the ground without damage to the blade or the tractor pushing it.
In conventional snowplows the presence of an obstacle projecting from the road surface, such as a curb, step, projecting drain cover or the like, that cannot be overcome by the snowplow scraper blade, gives rise to a hitch and causes enormous stress in the snow clearing blade and its supports so that the blade and its supports may be deformed and/or broken and/or the tractor may be damaged. To avoid this drawback, some conventional snowplows are provided with counteracting spring means generally comprising large helical springs adapted to normally keep the blade in the operative position, but yielding and permitting the snow clearing blade to tilt forwardly when the scraper blade at the lower edge of this blade knocks against an obstacle anchored to the ground, to permit the obstacle to be overcome. When the blade has cleared the obstacle, it returns to its operative position under the action of the springs.
But even with this safety means the problem of overcoming obstacles anchored to the ground cannot be solved in a satisfactory manner because the time of response of the counteracting spring means is too long and the apparatus and/or the tractor may be damaged in spite of the springs. Moreover, in many cases it is not sufficient for the blade to tilt forwardly to clear the obstacle. Finally, it often happens that when the spring constant of the return springs is so dimensioned that the spring will yield readily when the blade knocks against an obstacle, the spring will also permit the blade to tilt in normal operating conditions when the snow to be removed is too heavy and thick as in this case the resistance offered by the compressed coat of snow may cause the springs to yield when it is not required.